FIG. 4 shows a sectional view of a conventional linear motor disclosed in Japanese Patent Application Non-Examined Publication No. H11-313476. FIG. 5 shows a sectional view taken along the line 5—5 of FIG. 4.
Inner yoke 1 is formed by laminating a number of thin plates 2, each one of which has a high magnetic permeability and is in generally rectangular shape, into a prism. Outer yoke 3 is formed by laminating a number of thin plates 2, each one of which has a high magnetic permeability and slots 5, 6, and is in generally rectangular shape, into a prism. Coil 10 is wound on center magnetic pole 8, so that three magnetic poles 7, 8, 9 are formed. Inner yoke 1 and outer yoke 3 are apart from each other at a given gap 12 in between, and are fixed on yoke-block 11.
Movable section 14 is formed of a pair of permanent magnets 15, 16 disposed in gap 12, supporter 17 for supporting the permanent magnets, and output shaft 18. Permanent magnets 15, 16 are magnetized in different polarities from each other in the direction facing to outer yoke 3. Bearing 19 allows shaft 18 to reciprocate axially, and supports shaft 18 with the spin of shaft 18 regulated.
A flow of AC current through coil 10 generates an AC magnetic pole such as N-S-N or S-N-S in magnetic poles 7, 8, 9 of outer yoke 3. Magnetic attraction and repulsion between this AC magnetic pole and permanent magnets 15, 16 reciprocates movable section 14 axially.
In the foregoing structure; however, permanent magnets 15, 16 are supported only by supporter 17, so that movable section 14 is possibly deformed by magnetic force applied to the permanent magnets. Further, since there are air gaps on both sides of the permanent magnets, the magnetic fluxes of the permanent magnets are reduced.